Pectin is a naturally occurring substance found in the peel of citrus and other fruits; it is the jelling agent used in jams and jellies. Modified citrus pectin has been changed with heat and acid so that its long branched chains of sugars are broken down into smaller, non-branched chains of a simple sugar that is more digestible.
Slowing of tumor growth and spread has been reported in published animal studies, as well as a suggestion of possible cancer cell death (apoptosis). In a study of multiple myeloma cell lines, GCS-100, a derivative of citrus pectin, induced apoptosis in cells resistant to dexamethasone and other treatments. Delay of the prostate-specific-antigen (PSA) doubling time has been reported in a phase II pilot study of men with prostate cancer.
Link to additional reading
MCP in ACS site
MCP in Sloane Kettering site